The present invention relates to an instrument for insertion into an animal body, and, more particularly, concerns a catheter or probe for placement into various body orifices, and also concerns a method of inserting such an instrument into an animal body.
Medical instruments, intravascular catheters and the like probes are placed into various body orifices for many purposes, including the infusion of fluids, withdrawal of fluid samples from the body, and for the transduction of other parameters such as pressure, temperature and sound. Very often, such an instrument has to be placed in a remote part of the body or perhaps threaded for a considerable distance in the vascular system. Most catheters of the type for placement, particularly into a deep body position, are made of a pliable, very flexible, plastic material. This facilitates any bending or curving that is necessary during placement and also serves to eliminate or decrease the traumatic effect of its insertion. However, the relatively low flexural modulus of most catheters which provides the pliable nature of the catheter, produces at least one drawback.
A problem arises using most of the very flexible catheters during insertion of the same into the patient. The tendency of the catheter tubing to readily bend and flex during the insertion stage oftentimes produces awkward and erratic threading of the catheter by the operator. This is especially problematical when the catheter is long and is intended to be positioned deep in the patient.
Although some probe-like medical instruments have employed pressurization for various purposes, the variability of the flexural modulus to provide stiffness during insertion and then flexibility thereafter has not been disclosed. For instance, U.S. Pat. No. 3,525,329 discloses an evertable, extensible probe which admits pressure thereinto to extend the probe into the body cavity to be examined. Along the same lines, U.S. Pat. No. 3,502,069 employs a rigid tubular casing and a flexible evertable tubing inside. When fluid pressure is admitted into the casing the tubing is everted out of an open end of the casing. U.S. Pat. No. 3,168,092 describes a probing instrument with a tubing which becomes extraverted under pressure whereby the tubing exerts pressure on the walls of the cavity to separate the walls thereof.
Accordingly, it is most desirable to employ a catheter or like instrument which has a certain level of stiffness or increased flexural modulus of elasticity in order to facilitate placement of the catheter with relative ease into the patient. However, as pointed out above, after placement of the catheter into the final position the stiffness of the same is undesirable since more pliability and flexibility is required. It can be seen, then, that it is desirable to be able to vary the degree of stiffness of catheter tubing so as to have a relatively high degree of stiffness during placement of the catheter into the patient and then a relatively low degree of stiffness after final positioning. It is to this end that the present invention is directed.